Wireless power transfer

ABSTRACT

A power transmitter (101) provides power to a power receiver (105) via an electromagnetic power transfer signal. The power transmitter (101) comprises an output circuit (302, 103) with a transmitter coil (103) generating the power transfer signal in response to a drive signal generated by a driver (301). A configuration controller (303) switches between power transfer configurations having different maximum power limits and voltage amplitudes for the drive signal. A transmitter (307) transmits a power configuration message to the power receiver (105) comprising data indicative of a voltage amplitude for a first power transfer configuration a receiver (305) receives a power transfer configuration change request message from the power receiver (105). The configuration controller (303) switches the power transmitter (101) to the first power transfer configuration in response to the power transfer configuration change request message. The approach allows a power transmitter and receiver to collaborate to change power transfer configurations providing different maximum power limits.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§ 371 of International Application No. PCT/EP2020/050003, filed on Jan.2, 2020, which claims the benefit of EP Patent Application No. EP19152176.4, filed on Jan. 16, 2019. These applications are herebyincorporated by reference herein.

FIELD OF THE INVENTION

The invention relates to operation of a wireless power transfer systemand in particular, but not exclusively, to approaches for supportinghigher power levels in a wireless power transfer system such as Qi.

BACKGROUND OF THE INVENTION

Most present-day electrical products require a dedicated electricalcontact in order to be powered from an external power supply. However,this tends to be impractical and requires the user to physically insertconnectors or otherwise establish a physical electrical contact.Typically, power requirements also differ significantly, and currentlymost devices are provided with their own dedicated power supplyresulting in a typical user having a large number of different powersupplies with each power supply being dedicated to a specific device.Although, the use of internal batteries may avoid the need for a wiredconnection to a power supply during use, this only provides a partialsolution as the batteries will need recharging (or replacing). The useof batteries may also add substantially to the weight and potentiallycost and size of the devices.

In order to provide a significantly improved user experience, it hasbeen proposed to use a wireless power supply where power is inductivelytransferred from a transmitter coil in a power transmitter device to areceiver coil in the individual devices.

Power transmission via magnetic induction is a well-known concept,mostly applied in transformers having a tight coupling between a primarytransmitter inductor/coil and a secondary receiver coil. By separatingthe primary transmitter coil and the secondary receiver coil between twodevices, wireless power transfer between these becomes possible based onthe principle of a loosely coupled transformer.

Such an arrangement allows a wireless power transfer to the devicewithout requiring any wires or physical electrical connections to bemade. Indeed, it may simply allow a device to be placed adjacent to, oron top of, the transmitter coil in order to be recharged or poweredexternally. For example, power transmitter devices may be arranged witha horizontal surface on which a device can simply be placed in order tobe powered.

Furthermore, such wireless power transfer arrangements mayadvantageously be designed such that the power transmitter device can beused with a range of power receiver devices. In particular, a wirelesspower transfer approach, known as the Qi Specifications, has beendefined and is currently being developed further. This approach allowspower transmitter devices that meet the Qi Specifications to be usedwith power receiver devices that also meet the Qi Specifications withoutthese having to be from the same manufacturer or having to be dedicatedto each other. The Qi standard further includes some functionality forallowing the operation to be adapted to the specific power receiverdevice (e.g. dependent on the specific power drain).

The Qi Specification is developed by the Wireless Power Consortium andmore information can e.g. be found on their website:http://www.wirelesspowerconsortium.com/index.html, where in particularthe defined Specification documents can be found.

Qi originally in version 1.0 defined low power wireless power transferwhich in practice was limited to lower power levels below 5 W. This hasbeen extended to higher power levels in subsequent versions, and version1.2. e.g. providing compliance testing addressed at power levels up to15 W.

However, it is desired to support even higher power levels andproprietary solutions have been introduced in some cases in order toachieve this. However, most suggested approaches for supporting highpower level wireless power transfer tend to be suboptimal and a numberof challenges or undesired effects can occur. For example, supporting alarge power range is challenging. E.g. variations in the provided powermay be difficult to control over a large range merely by adjusting orlimiting current being provided to a power transmitter coil. Anotherchallenge is to ensure that the effects and consequences of changingoperating parameters and conditions e.g. when changing power levels areacceptable and e.g. can be handled by the power receiver. For example, asubstantial and quick change in the drive voltage may result in atransient in the voltage induced at the power receiver therebypotentially causing an overvoltage (or undervoltage) situation.

Hence, an improved approach for wireless power transfer would beadvantageous, in particular, an approach allowing increased flexibility,reduced cost, reduced complexity, improved support for large powerranges, improved transient power performance, improved adaptability,backwards compatibility, improved power transfer operation, and/orimproved performance would be advantageous.

SUMMARY OF THE INVENTION

Accordingly, the Invention seeks to preferably mitigate, alleviate oreliminate one or more of the above mentioned disadvantages singly or inany combination.

According to an aspect of the invention there is provided a powertransmitter for wirelessly providing power to a power receiver via anelectromagnetic power transfer signal; the power transmitter comprising:a transmitter coil for generating the power transfer signal in responseto a drive signal being applied to the transmitter coil; a driver forgenerating the drive signal; a configuration controller for switchingbetween a set of power transfer configurations, the power transferconfigurations of the set of power transfer configurations havingdifferent combinations of a maximum power limit and a voltage amplitudefor the drive signal; a transmitter for transmitting a powerconfiguration message to the power receiver, the power configurationmessage comprising data indicative of a voltage amplitude for a firstpower transfer configuration of the set of power transferconfigurations; a receiver for receiving a power transfer configurationchange request message from the power receiver; and wherein theconfiguration controller is arranged to switch the power transmitter tothe first power transfer configuration in response to the power transferconfiguration change request message.

The invention may provide improved performance and/or improved powertransfer in many scenarios. It may in many embodiments allow an improvedand more efficient power transfer over a large range of power levels.The approach may in many embodiments support, enable, improve, orfacilitate high power wireless power transfer.

In many embodiments, an improved switching between different powertransfer configurations may be achieved, and in particular the impact oftransient conditions and changes in the power transfer parameters mayoften be mitigated. Specifically, in many embodiments and scenarios,improved transient undervoltage/overvoltage operation may be achieved.

The set of power transfer configurations may have different combinationsof a maximum power limit and a voltage amplitude for the drive signal inthe sense that at least one of a maximum power limit and a voltageamplitude is different for different power transfer configurations ofthe set of power transfer configurations.

The first power transfer configuration is a candidate power transferconfiguration. The first power transfer configuration is different froma current power transfer configuration (being the power transferconfiguration the power transmitter is currently working in).

The configuration controller may be arranged to switch the powertransmitter from a current power transfer configuration to the firstpower transfer configuration in response to the power transferconfiguration change request message. The configuration controller maybe arranged to switch the power transmitter to the first power transferconfiguration in response to receiving the power transfer configurationchange request message. The power transfer configuration change requestmessage may request a change from a current power transfer mode to thefirst power transfer mode.

The output circuit may comprise or consist in a resonance (or tank)circuit comprising the transmitter coil. The transmitter coil may be aresonating component of the resonance circuit. The resonance circuit maybe a series resonance circuit or a parallel resonance circuit. Theresonance circuit may include one or more capacitors.

The voltage amplitude may e.g. be a peak-to-peak voltage amplitude, apeak amplitude and/or a semi-amplitude. In some embodiments, and forsome signals, the voltage amplitude may for example be an effective orroot-mean square amplitude.

The voltage amplitude for a power transfer configuration may be aconstant voltage amplitude for the drive signal. The power transmittermay be arranged to control a power level of the power transfer signal byvarying at least one of a frequency, duty cycle and a current amplitudeof the drive signal. The voltage amplitude may be constant/fixed for agiven power transfer configuration.

In some embodiments, the voltage amplitude for a power transferconfiguration may be a range of the voltage amplitude for the drivesignal. For example, the voltage amplitude for each power transferconfiguration may be a maximum voltage amplitude limit and/or a minimumvoltage amplitude limit. In some embodiments, the voltage amplitude forthe first power transfer configuration provided in the powerconfiguration message may be an indication of a voltage amplitude rangeand/or a maximum/minimum voltage amplitude limit for the first powertransfer configuration. In some embodiments, the voltage amplitude forthe first power transfer configuration provided in the powerconfiguration message may be an indication of a nominal or initialvoltage amplitude for the drive signal after switching to the firstpower transfer configuration.

In accordance with an optional feature of the invention, the data isindicative of a relative difference between the voltage amplitude forthe first power transfer configuration and a voltage amplitude for acurrent power transfer configuration.

This may provide improved performance in many embodiments. It may allowa more efficient trade-off between accuracy and communication bandwidthin many embodiments, and may provide particularly relevant informationfor the transient performance when changing power transferconfigurations.

In accordance with an optional feature of the invention, the data isindicative of a ratio between the voltage amplitude for the first powertransfer configuration and the voltage amplitude for the current powertransfer configuration.

This may provide improved performance in many embodiments. It may allowa more efficient trade-off between accuracy and communication bandwidthin many embodiments and may provide particularly relevant informationfor the transient performance when changing power transferconfigurations.

In accordance with an optional feature of the invention, the first powertransfer configuration is a power transfer configuration of the set ofpower transfer configurations having a maximum power limit being atleast one of the next higher maximum power limit and the next lowermaximum power limit for a maximum power limit of a current powertransfer configuration.

This may provide particularly efficient operation in many embodiments.It may particularly provide an efficient approach for controllingdynamic power level variation which may support a large range of powerlevels yet maintain low communication requirements. It may restrict thepower level changes to reduce transient properties and/or reduce thecommunication requirement e.g. by enabling that no further informationthan the voltage amplitude need to be provided for candidate powertransfer configurations.

In accordance with an optional feature of the invention, the powerconfiguration message comprises data indicative of a voltage amplitudefor a second power transfer configuration of the set of power transferconfigurations, the first power transfer configuration being a powertransfer configuration of the set of power transfer configurationshaving a maximum power limit being a next higher maximum power limit fora maximum power limit of a current power transfer configuration and thesecond power transfer configuration being a power transfer configurationof the set of power transfer configurations having a maximum power limitbeing the next lower maximum power limit for the maximum power limit ofthe current power transfer configuration.

This may provide particularly efficient operation in many embodiments.The power mode message may specifically provide the information for theclosest (in terms of maximum power limit) power transfer configurationsavailable to the power transmitter for respectively increasing anddecreasing the power level.

In accordance with an optional feature of the invention, a predeterminedvalue of the data indicative of the voltage amplitude indicates that theset of power transfer configurations does not comprise a power transferconfiguration that has a higher maximum power limit than a maximum powerlimit of a current power transfer configuration.

This may allow a particularly efficient communication of theavailability of power transfer configurations.

In some embodiments, a predetermined value of the data indicative of thevoltage amplitude indicates that the set of power transferconfigurations does not comprise a power transfer configuration that hasa lower maximum power limit than a maximum power limit of a currentpower transfer configuration.

This may allow a particularly efficient communication of theavailability of power transfer configurations.

In some embodiments, a predetermined value of the data indicative of thevoltage amplitude is indicative of there being no change in the voltageamplitude for the first power transfer configuration relative to avoltage amplitude for a current power transfer configuration.

In accordance with an optional feature of the invention, theconfiguration controller is arranged to transmit the power configurationmessage in response to a detection that an operating characteristic ofthe power transfer meets a criterion.

This may provide a particularly advantageous performance and operationin many embodiments. The approach may support power transmitterinitiated change of the power transfer configuration while ensuring thatthis is done in collaboration with the power receiver thereby reducingthe risk of undesired effects at the power receiver.

The operating characteristics of the power transfer may specifically bea parameter indicative of a current power level of the power transfersignal (for the current power transfer configuration), such as e.g. aparameter indicative of a frequency or a current of the drive signal.

In accordance with an optional feature of the invention, theconfiguration controller is arranged to transmit the power configurationmessage in response to a detection that a current power level of thepower transmitter exceeds a threshold, the threshold being dependent ona maximum power limit of a current power transfer configuration.

This may provide a particularly advantageous performance and operationin many embodiments. The approach may support power transmitterinitiated change of the power transfer configuration while ensuring thatthis is done in collaboration with the power receiver thereby reducingthe risk of undesired effects at the power receiver.

In accordance with an optional feature of the invention, theconfiguration controller is arranged to transmit the power configurationmessage in response to receiving a power configuration informationrequest message from the power receiver.

This may provide a particularly advantageous performance and operationin many embodiments. The approach may support power receiver initiatedchange of the power transfer configuration while ensuring that this isdone in collaboration with the power transmitter.

In accordance with an optional feature of the invention, theconfiguration controller is arranged to switch the power transmitter tothe first power transfer configuration after having transmitted anacknowledgement message to the power receiver, the acknowledgementmessage acknowledging a request message received from the powerreceiver.

This may provide a particularly advantageous performance and operationin many embodiments.

According to an aspect of the invention there is provided a powerreceiver for wirelessly receiving power from a power transmitter via anelectromagnetic power transfer signal, the power receiver comprising: aninput circuit comprising a power receiver coil arranged to extract powerfrom the power transfer signal; a receiver for receiving a powerconfiguration message from the power transmitter, the powerconfiguration message comprising data indicative of a voltage amplitudeof a drive signal for at least a first power transfer configuration of aset of power transfer configurations, the power transfer configurationsof the set of power transfer configurations having differentcombinations of a maximum power limit and a voltage amplitude and thedrive signal being for an output circuit of the power transmittercomprising a transmitter coil for generating the power transfer signalin response to the drive signal being applied to the output circuit; aconfiguration controller arranged to detect a power transferconfiguration change preference for the power transmitter to switch tothe first power transfer configuration; and a transmitter fortransmitting a power transfer configuration change request message tothe power transmitter in response to the detection of the power transferconfiguration change preference, the power transfer configuration changerequest message comprising a request for the power transmitter to switchto the first power transfer configuration.

In accordance with an optional feature of the invention, theconfiguration controller is arranged to control the power transfer tochange a voltage induced over the power receiver coil in advance of achange in power transfer configuration to the first power transferconfiguration.

This may provide a particularly advantageous performance and operationin many embodiments. It may in many scenarios compensate or mitigatetransient voltage variations and e.g. prevent undervoltage orovervoltage conditions.

In accordance with an optional feature of the invention, theconfiguration controller is arranged to change a load impedance for thepower receiver coil in advance of a change in power transferconfiguration to the first power transfer configuration.

This may provide a particularly advantageous performance and operationin many embodiments.

According to an aspect of the invention there is provided a method ofoperation of a power transmitter wirelessly providing power to a powerreceiver via an electromagnetic power transfer signal; the methodcomprising: a transmitter coil generating the power transfer signal inresponse to a drive signal being applied to the transmitter coil;generating the drive signal; switching between a set of power transferconfigurations, the power transfer configurations of the set of powertransfer configurations having different combinations of a maximum powerlimit and a voltage amplitude for the drive signal; transmitting a powerconfiguration message to the power receiver, the power configurationmessage comprising data indicative of a voltage amplitude for a firstpower transfer configuration of the set of power transferconfigurations; receiving a power transfer configuration change requestmessage from the power receiver; and wherein the switching between theset of power transfer configurations switches the power transmitter tothe first power transfer configuration in response to the power transferconfiguration change request message.

According to an aspect of the invention there is provided a method ofoperation of a power receiver wirelessly receiving power from a powertransmitter via an electromagnetic power transfer signal, the methodcomprising: a power receiver coil extracting power from the powertransfer signal; receiving a power configuration message from the powertransmitter, the power configuration message comprising data indicativeof a voltage amplitude of a drive signal for at least a first powertransfer configuration of a set of power transfer configurations, thepower transfer configurations of the set of power transferconfigurations having different combinations of a maximum power limitand a voltage amplitude and the drive signal being for an output circuitof the power transmitter comprising a transmitter coil for generatingthe power transfer signal in response to the drive signal being appliedto the output circuit; detecting a power transfer configuration changepreference for the power transmitter to switch to the first powertransfer configuration; and transmitting a power transfer configurationchange request message to the power transmitter in response to thedetection of the power transfer configuration change preference, thepower transfer configuration change request message comprising a requestfor the power transmitter to switch to the first power transferconfiguration.

According to another aspect of the invention, there is provided awireless power transfer system for wirelessly providing power to a powerreceiver from a power transmitter via an electromagnetic power transfersignal; the power transmitter comprising: an output circuit comprising atransmitter coil for generating the power transfer signal in response toa drive signal being applied to the output circuit; a driver forgenerating the drive signal; a configuration controller for switchingbetween a set of power transfer configurations, the power transferconfigurations of the set of power transfer configurations havingdifferent combinations of a maximum power limit and a voltage amplitudefor the drive signal; a transmitter for transmitting a powerconfiguration message to the power receiver, the power configurationmessage comprising data indicative of a voltage amplitude for a firstpower transfer configuration of the set of power transferconfigurations; a receiver for receiving a power transfer configurationchange request message from the power receiver; and wherein theconfiguration controller is arranged to switch the power transmitter tothe first power transfer configuration in response to the power transferconfiguration change request message; and the power receiver comprising:an input circuit comprising a power receiver coil arranged to extractpower from the power transfer signal; a receiver for receiving the powerconfiguration message from the power transmitter, a configurationcontroller arranged to detect a power transfer configuration changepreference for the power transmitter to switch to the first powertransfer configuration; and a transmitter for transmitting the powertransfer configuration change request message to the power transmitterin response to the detection of the power transfer configuration changepreference, the power transfer configuration change request messagecomprising a request for the power transmitter to switch to the firstpower transfer configuration.

These and other aspects, features and advantages of the invention willbe apparent from and elucidated with reference to the embodiment(s)described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only,with reference to the drawings, in which

FIG. 1 illustrates an example of elements of a power transfer system inaccordance with some embodiments of the invention;

FIG. 2 illustrates an example of a set of power transfer configurationsfor a power transmitter in accordance with some embodiments of theinvention;

FIG. 3 illustrates an example of elements of a power transmitter inaccordance with some embodiments of the invention;

FIG. 4 illustrates an example of elements of an output stage of a powertransmitter;

FIG. 5 illustrates an example of elements of an output stage of a powertransmitter;

FIG. 6 illustrates an example of elements of a power receiver inaccordance with some embodiments of the invention;

FIG. 7 illustrates an example of a power configuration message inaccordance with some embodiments of the invention;

FIG. 8 illustrates an example of a power transfer configuration changerequest message in accordance with some embodiments of the invention;

FIG. 9 illustrates an example of a message exchange in accordance withsome embodiments of the invention; and

FIG. 10 illustrates an example of a message exchange in accordance withsome embodiments of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following description focuses on embodiments of the inventionapplicable to a wireless power transfer system utilizing a powertransfer approach such as known from the Qi specification. However, itwill be appreciated that the invention is not limited to thisapplication but may be applied to many other wireless power transfersystems.

FIG. 1 illustrates an example of a power transfer system in accordancewith some embodiments of the invention. The power transfer systemcomprises a power transmitter 101 which includes (or is coupled to) atransmitter coil/inductor 103. The system further comprises a powerreceiver 105 which includes (or is coupled to) a receiver coil/inductor107.

The system provides an electromagnetic power transfer signal which mayinductively transfer power from the power transmitter 101 to the powerreceiver 105. Specifically, the power transmitter 101 generates anelectromagnetic signal, which is propagated as a magnetic flux by thetransmitter coil or inductor 103 (which is typically part of an outputcircuit in the form of a resonance or tank circuit). The power transfersignal may correspond to the electromagnetic power transfer componentrepresenting the energy transfer from the power transmitter to the powerreceiver, and may be considered to correspond to the component of thegenerated electromagnetic field that transfers power from the powertransmitter to the power receiver. For example, if there is no loadingof the receiver coil 107, no power will be extracted by the powerreceiver from the generated electromagnetic field (apart from losses).In such a scenario, the driving of the transmitter coil 103 may generatean electromagnetic field of potentially high field strength but thepower level of the power transfer signal will be zero (apart fromlosses). In some situations, where a foreign object is present, thepower transfer signal may be considered to include a componentcorresponding to the power transfer to the foreign object, and thus thepower transfer signal may be considered to correspond to the power beingextracted from the electromagnetic field generated by the powertransmitter.

The power transfer signal may typically have a frequency between around20 kHz to around 500 kHz, and often for Qi compatible systems typicallyin the range from 95 kHz to 205 kHz (or e.g. for high power kitchenapplications, the frequency may e.g. typically be in the range between20 kHz to 80 kHz). The transmitter coil 103 and the power receiving coil107 are loosely coupled and thus the power receiving coil 107 picks up(at least part of) the power transfer signal from the power transmitter101. Thus, the power is transferred from the power transmitter 101 tothe power receiver 105 via a wireless inductive coupling from thetransmitter coil 103 to the power receiving coil 107. The term powertransfer signal is mainly used to refer to the inductive signal/magneticfield between the transmitter coil 103 and the power receiving coil 107(the magnetic flux signal).

In the example, the power receiver 105 is specifically a power receiverthat receives power via the receiver coil 107. However, in otherembodiments, the power receiver 105 may comprise a metallic element,such as a metallic heating element, in which case the power transfersignal directly induces eddy currents resulting in a direct heating ofthe element.

The system is arranged to transfer substantial power levels, andspecifically the power transmitter may support power levels in excess of500 mW, 1 W, 5 W, 50 W, 100 W or 500 W in many embodiments. For example,for Qi corresponding applications, the power transfers may typically bein the 1-5 W power range for low power applications (the baseline powerprofile), up to 15 W for Qi specification version 1.2, in the range upto 100 W for higher power applications such as power tools, laptops,drones, robots etc., and in excess of 100 W and up to more than 1000 Wfor very high-power applications, such as e.g. kitchen applications.

In the following, the operation of the power transmitter 101 and thepower receiver 105 will be described with specific reference to anembodiment generally in accordance with the Qi Specification (except forthe herein described (or consequential) modifications and enhancements)or suitable for the higher power kitchen specification being developedby the Wireless Power Consortium. In particular, the power transmitter101 and the power receiver 105 may follow, or substantially becompatible with, elements of the Qi Specification version 1.0, 1.1 or1.2 (except for the herein described (or consequential) modificationsand enhancements).

The system of FIG. 1 is arranged to support power transfer with a largerange of power levels. The system supports this by the power transmitterbeing able to operate in a plurality of different power transferconfigurations with these corresponding to different power levels.

Specifically, some of power transfer configurations use differentvoltage amplitudes for driving output circuit with the transmitter coil103. Conventionally, the output circuit is a series resonance circuitwith the transmitter coil forming the inductive resonating component andwith the series resonance circuit being driven by a drive signal with aconstant voltage amplitude and with the power level being determined andvaried by varying the current provided to the output circuit, eitherdirectly or indirectly, e.g. by varying a drive frequency or duty cycleof the drive signal. However, large power level variations becomedifficult to support in this way as the required variation in thecurrent becomes difficult to achieve and control. Accordingly, thesystem of FIG. 1 allows the power transmitter 101 to switch betweendifferent power transfer configurations which may correspond todifferent maximum power limits and use different voltage amplitudes forthe drive signal to the transmitter coil 103. Specifically, for a givenpower transfer configuration, the voltage amplitude of the drive signalmay be constant but the voltage amplitude may be different for differentpower transfer configurations. The maximum power limit may be an upperlimit on the power of power transfer signal that is supported when inthe current power transfer configuration. The power limit may be imposedby restricting a current of the drive signal provided to the transmittercoil 103. Thus, a maximum power limit may correspond to a maximumcurrent limit.

The voltage amplitude may be a peak-to-peak, a peak, or a semi-amplitudefor the drive signal, and the drive signal may in many embodiments be asquare wave or a rectangular wave. Specifically, the drive signal may bea signal which has a value of either +Va, −Voltage amplitude, or 0,where Va is the (peak) voltage amplitude. The drive signal may have meanof 0. In some embodiments, the drive signal may be a different waveformsuch as e.g. a sine wave, a triangular wave etc.

Thus, the power transmitter 101 may be arranged to operate in one of aplurality of power transfer configurations where each power transferconfiguration specifically may correspond to a different combination ofa drive signal voltage amplitude and a maximum power limit (and thus amaximum current limit). For example, is illustrated in FIG. 2 , thepower transmitter 101 may be arranged to operate in one out of ndifferent power transfer configurations with each configuration havingan associated maximum power limit and a fixed drive signal voltageamplitude. For example, the power transmitter 101 may be arranged toselect a current power transfer configuration from a set of powertransfer configurations having the following maximum powerlimits/maximum current limits and drive signal voltage amplitudes (inthe example the effective values of the voltage amplitude and maximumcurrent limit are provided).

-   -   5 V, 1.5 A (7.5 W)    -   9V, 1 A (9 W)    -   5 V, 2 A (10 W)    -   12 V, 1 A (12 W)    -   9 V, 2 A (18 W)    -   12 V, 1.5 A (18 W)    -   19 V, 1 A (19 W)    -   12 V, 2 A (24 W)    -   19 V, 2 A (38 W)    -   19 V, 3 A (57 W)

The power transmitter 101 may thus be arranged to operate in one of aset of power transfer configurations with different voltage amplitudes,where higher voltage amplitudes are needed to achieve higher powerlevels.

FIG. 3 illustrates elements of the power transmitter 101 of FIG. 1 inmore detail.

The power transmitter 101 includes a driver 301 which can generate adrive signal that is fed to an output circuit which in the example is aresonance circuit formed by the transmitter coil 103 and a transmittercapacitor 302. The transmitter coil 103 in return to being driven by thedrive signal generates an electromagnetic field and thus theelectromagnetic power transfer signal which provides power transfer tothe power receiver 105. The power transfer signal is provided (at least)during a power transfer phase.

The driver 301 is typically a drive circuit in the form of an inverterwhich generates an alternating signal from a DC Voltage. The output ofthe driver 301 is typically a switch bridge generating the drive signalby the appropriate switching of switches of the switch bridge. FIG. 4shows a half-bridge switch bridge/inverter. The switches S1 and S2 arecontrolled such that they are never closed at the same time.Alternatingly S1 is closed while S2 is open and S2 is closed while S1 isopen. The switches are opened and closed with the desired frequency,thereby generating an alternating signal at the output. Typically, theoutput of the inverter is connected to the transmitter inductor via aresonance capacitor. FIG. 5 shows a full-bridge switch bridge/inverter.The switches S1 and S2 are controlled such that they are never closed atthe same time. The switches S3 and S4 are controlled such that they arenever closed at the same time. Alternatingly switches S land S4 areclosed while S2 and S3 are open, and then S2 and S3 are closed while S1and S4 or open, thereby creating a square-wave signal at the output. Theswitches are open and closed with the desired frequency.

The driver 301 thus generates a drive signal for the output resonancecircuit and thus for the transmitter coil 103. The drive signal has a(substantially) constant voltage amplitude for a given power transferconfiguration. In the example, the constant voltage amplitude isachieved by setting a constant rail voltage for the output circuit ofthe driver, i.e. the rail voltage V for the bridges of FIGS. 4 and 5 isconstant for a given power transfer configuration. The switching by thebridge transistors respectively switches the output voltage between 0and V for the half bridge and between V and −V for the full bridge.Thus, in the example the power transmitter may set the rail voltage tobe constant for any given power transfer configuration but to (possibly)vary between power transfer configurations.

The power transmitter 101 further comprises a power transmittercontroller 303 which is arranged to control the operation of the powertransmitter 101 in accordance with the desired operating principles.Specifically, the power transmitter 101 may include many of thefunctionalities required to perform power control in accordance with theQi Specifications.

The power transmitter controller 303 is in particular arranged tocontrol the generation of the drive signal by the driver 301. The powertransmitter controller 303 may specifically set the rail voltage for thedrive corresponding to the specific power transfer configuration inwhich the power transmitter is currently operating.

The power transmitter controller 303 may further dynamically control thepower level of the drive signal, and thus of the power transfer signalgenerated by the transmitter coil 103. The power transmitter controller303 specifically comprises a power loop controller controlling a powerlevel of the power transfer signal in response to power control messagesreceived from the power receiver 105 during the power control phase. Thecontrol of the power level may specifically be achieved by controlling acurrent of the drive signal or more typically by controlling a dutycycle or frequency of the drive signal. In the latter example, the powerlevel may be increased by shifting the frequency closer to a resonancefrequency for the output resonance circuit comprising the transmittercoil 103 (and/or a resonance frequency of a resonance circuit of thepower receiver 105 which includes the receiver coil 107) and decreasedby shifting the frequency further away from the resonance frequency.

In addition, the power transmitter controller 303 may for a given powertransfer configuration limit the power level to a maximum power level.This is typically done by limiting the current of the drive signal. Thecurrent may be actively limited or in some embodiments, the maximumpower limit may be indirect (potentially even unintentional) and e.g.due to a practical limit on the current that can be provided to thedriver by a power supply. In some embodiments, the maximum power limitmay be a restriction imposed by the control algorithm e.g. in order toensure that the thermal capabilities of the switch-bridge transistorsare not exceeded. For example, for a system wherein the power level iscontrolled by controlling the frequency and/or duty cycle of the drivesignal/power transfer signal, the controller may continuously monitorthe power level and adapt the frequency subject to a requirement thatthe power level does not exceed the maximum power limit for the currentpower transfer configuration.

In order to receive data and messages from the power receiver 105, thepower transmitter 101 comprises a first receiver 305 which is arrangedto receive data and messages from the power receiver 105 (as will beappreciated by the skilled person, a data message may provide one ormore bits of information). In the example, the power receiver 105 isarranged to load modulate the power transfer signal generated by thetransmitter coil 103, and the first communicator 305 is arranged tosense variations in the voltage and/or current of the transmitter coil103 and to demodulate the load modulation based on these. The skilledperson will be aware of the principles of load modulation, as e.g. usedin Qi wireless power transfer systems, and therefore these will not bedescribed in further detail.

The power transmitter 101 further arranged to transmit data to the powerreceiver 105 and accordingly comprises a first transmitter 307 which isarranged to transmit data to the power receiver e.g. by specificallymodulating the drive signal and thus the power transfer signal usingfrequency, amplitude, and/or phase modulation.

It will be appreciated that other approaches for communicating databetween the power transmitter 101 and the power receiver 105 may be usedin other embodiments. For example, in some embodiments, communicationmay be performed using a separate communication channel which may beachieved using a separate communication coil, or indeed using thetransmitter coil 103. For example, in some embodiments Near FieldCommunication may be implemented or a high frequency carrier (e.g. witha carrier frequency of 13.56 MHz) may be overlaid on the power transfersignal.

The power transmitter 101 further comprises a first configurationcontroller 309 which is arranged to control which power transferconfiguration the power transmitter 101 is operating in, and thusspecifically is arranged to switch the power transmitter 101 between thedifferent power transfer configurations of the set of possible powertransfer configurations.

FIG. 6 illustrates some exemplary elements of the power receiver 105.

The receiver coil 107 is coupled to a power receiver controller 601which couples the receiver coil 107 to a load 603. The power receivercontroller 601 includes a power control path which converts the powerextracted by the receiver coil 107 into a suitable supply for the load.In addition, the power receiver controller 601 may include various powerreceiver controller functionality required to perform power transfer,and in particular functions required to perform power transfer inaccordance with the Qi specifications.

The power receiver 105 further comprises a second receiver 605 which isarranged to receive data transmitted from the power transmitter 101. Inthe example, the second receiver 605 is arranged to demodulateamplitude, frequency, and/or phase modulation of the power transfersignal as appropriate in order to retrieve data transmitted from thepower transmitter.

In order to support communication from the power receiver 105 to thepower transmitter 101, the power receiver 105 comprises a secondtransmitter 607. The second transmitter 607 is arranged to transmit datato the power transmitter by varying the loading of the receiver coil 107in response to data to be transmitted to the power transmitter 101. Theload variations are then detected and demodulated by the powertransmitter 101 as will be known to the person skilled in the art.

As previously mentioned, in other embodiments other communicationmethods may be used, such as e.g. a separate and dedicated short rangecommunication approach such as NFC may be used.

The power receiver 105 further comprises a second configurationcontroller 609 which is arranged to support the use of different powertransfer configurations, and specifically it may support and control theswitching of the power transmitter 101 between different power transferconfigurations.

Thus, in the system of FIG. 1 , a range of different power transferconfigurations with different maximum power levels may be used for thepower transfer thereby providing for a potentially large range of powerlevels being supported including quite high power levels. Further, thepower transmitter and power receiver may be arranged to dynamicallyswitch between different power configurations. For example, a powertransfer operation may initially start at a low power level and thengradually increase the power level to increasingly higher level. Forexample, charging a large capacity battery may for safety start at lowercharging levels and then increase to a potentially high level with ahigh charge current when it is ensured that this can be safely supported(e.g. ensuring that there are no foreign metallic objects in theneighborhood). Similarly, in many embodiments, the load 603 may be avariable load that has a highly variable power consumption. For example,the load may be a device including an engine running onlyintermittently. Thus, in many situations, it may be desirable to changebetween different power transfer configurations with the changes beingpotentially both unpredictable and in both a power increasing and powerdecreasing direction.

However, whereas this may allow an improved performance over a largerpower range in many embodiments, the Inventor has further realized thatthere are potential risks and difficulties in changing between differentpower transfer configurations with different drive voltages for thedrive signal.

In particular, a change in the voltage of the drive signal may result ina step/transient in the induced voltage at the receiver coil 107. Thus,the switch from one power transfer configuration to another may cause anundervoltage or an overvoltage condition to occur at the power receiver.For some power receivers and in some situations, such an undervoltage orovervoltage condition may be fully acceptable and not have anysignificant impact on the operation. However, for other power receiversand/or in other scenarios, the undervoltage and/or overvoltage may havea significant effect and may cause suboptimal or even erroneousoperation. Indeed, in some situations, it can even be envisaged thatdamage to the power receiver may result from an overvoltage condition ifsuitable precautions are not taken.

As a specific example, the power transmitter may be operating in a 10 W(5 V, 2 A) configuration, with the power receiver controlling itsoperating point to 8 V, 1 A. When the power transmitter switches to anext higher configuration, such as 12 W (12V, 1 A), the power receiverwould initially see a voltage of 12/5*8=19.5 V, 2.4 A, which his farbeyond the capability of the power transmitter in this configuration.Accordingly, the power transfer may collapse due to the over voltage orover-power condition being generated.

A similar situation can occur when switching to a lower-powerconfiguration. For example, if the power transmitter operates in a 12V,1 A configuration, and the power receiver takes only 4 W (e.g. 5 V, 0.8A), it may be more advantageous to switch to a next-lower configurationon the power transmitter, e.g. 5. V1.5 A. Were this switch to be madewithout the power receiver preparing, it would experience a voltage of5/12*5=2.1 V after the switch, which could be too low to sustain itsoperations (i.e. under voltage). Accordingly, this would result in acollapse of the power transfer as well.

In the approach of FIG. 1 , a particular approach for switching betweenpower transfer configurations is implemented which can provide improvedperformance in many embodiments. The approach allows the powertransmitter and the power receiver to interwork in order to carefullycontrol the switching of power transfer configuration, and specificallysuch that the power receiver is aware of, and typically fully controls,the switching from one power transfer configuration to another therebypreventing unpredicted under- or overvoltage conditions arising.

The approach is based on the power transmitter and power receiverexchanging information in order to control and coordinate changes in thepower transfer configuration. The message exchange may specificallyallow the power receiver to control the change in the power transferconfiguration for the power transmitter such that this can be ensured toproceed without the change resulting in an unacceptable impact at thepower receiver (it may e.g. allow the power receiver to compensate forthe effects).

Thus, in the example, the power transmitter 101 comprises a firstconfiguration controller 309 which is arranged to control the powertransmitter 101 to operate in a power transfer configuration selectedfrom a set of a plurality of power transfer configurations each of whichmay represent a different combination of a (substantially) constantvoltage amplitude of a drive signal for the output circuit including thetransmitter coil 103 and a maximum power limit of the power transfersignal/drive signal. The power transmitter 101 is furthermore arrangedto transmit a power configuration message to the power receiver 105which comprises data indicative of a voltage amplitude for the drivesignal for one or more power transfer configurations of the set of powertransfer configurations.

The power configuration message may specifically include data describingthe voltage amplitude for the power transfer configuration for one ormore candidate power transfer configurations to which the powertransmitter 101 can potentially switch. In many embodiments, the powerconfiguration message may specifically provide voltage amplitudeinformation for a next higher and/or next lower power transferconfiguration in a given (e.g. predetermined or previously communicated)sequence of the power transfer configurations that the power transmitter101 may operate in. For example, the power transfer configurations maybe ordered in order of the maximum power limit (and in order of voltageamplitude in case some power transfer configurations have the samemaximum power limit), and the power configuration message may indicatethe value of the next higher and lower power transfer configuration inaccordance with this sequence. The power configuration message mayaccordingly provide the voltage amplitude for the immediately highermaximum power limit and the immediately lower maximum power limit.

The voltage indication may be given as an absolute value or e.g. as arelative value with respect to the voltage amplitude of the currentpower transfer configuration.

In the approach, the power receiver 105 may accordingly be provided withinformation of the power transfer configurations to which the powertransmitter can switch.

The second receiver 605 of the power receiver 105 may receive the powerconfiguration message and the power receiver 105 accordingly informed ofthe potential changes in the power transfer configuration and of theresulting changes in the voltage amplitude. Accordingly, the powerreceiver has information that allows it to evaluate the result of aconsequent change in the power transfer configuration.

Further, the power receiver 105 comprises a second configurationcontroller 609 which is arranged to detect a power transferconfiguration preference for the power transmitter to switch to (one of)the power transfer configuration(s) indicated by the power configurationmessage.

The desire/request/preference to change the power transfer configurationmay be detected in any suitable way and using any suitablealgorithm/criterion. The approach does not depend on any specificapproach or requirement, or indeed where the preference is determined,by which function, or indeed by which device or apparatus. The approachis thus based on the second configuration controller 609 detecting thatthere exists a preference for changing the power transfer configurationbut is not reliant on where, why, or how this preference originates.

The preference may in many embodiments be determined in the powerreceiver 105 and specifically by the second configuration controller609. For example, the second configuration controller 609 may determinethat the power transfer is operating close to the maximum power limitfor the current power transfer configuration and that there is a demandfor increased power, and thus a preference to switch to a power transferconfiguration with a higher maximum power limit.

In some embodiments, the preference to switch to a different powertransfer configuration may e.g. be determined by the power transmitterand the second configuration controller 609 may detect this preferencee.g. in response to a property of the power transfer signal or tocommunication from the power transmitter. For example, the powertransmitter may transmit a request for a power transfer configurationchange to the power receiver when the power transmitter determines thatsuch a switch would be desirable. Indeed, in many embodiments, the powertransmitter may be arranged to transmit the power configuration messagein response to the power transmitter determining that there is apreference to change the power transfer configuration, and thus thepower configuration message may itself be a power transfer configurationchange request message.

The second transmitter 607 may be arranged to transmit a power transferconfiguration change request message to the power transmitter inresponse to the detection of the power transfer configuration changepreference. In many embodiments, the transmission may be conditional,such as specifically conditional on the voltage amplitude for thecorresponding power transfer configuration meeting a criterion.

For example, the second configuration controller 609 may in response todetecting that there is a desire to change the power transferconfiguration to a given candidate power transfer configuration evaluateif the change to that candidate power transfer configuration will resultin an unacceptable undervoltage or overvoltage condition occurring atthe power receiver as a result of the switch. As a simple example, thesecond configuration controller 609 may simply determine whether theratio between the voltage amplitude of the current power transferconfiguration and the voltage amplitude of the candidate power transferconfiguration exceeds a threshold which is considered acceptable to thespecific power receiver (in the specific circumstances). If so, thesecond transmitter 607 may proceed to transmit the power transferconfiguration change request message to the power transmitter andotherwise no power transfer configuration change request message istransmitted.

In other embodiments, the second transmitter 607 may be arranged toalways transmit the power transfer configuration change request messageto the power transmitter 101 if a power transfer configuration changepreference is detected. In such embodiments, the power receiver 105 maybe arranged to adapt an operation or configuration of the power receiver105 in response to the voltage amplitude of the requested power transferconfiguration, and typically in response to a relationship between thevoltage amplitude of the requested power transfer configuration and thevoltage amplitude of the current power transfer configuration.

For example, if the voltage amplitude change is sufficiently small, noproblematic under- or over-voltage condition will occur and accordinglyno change in operation or configuration may be needed. However, if thechange in voltage amplitude is sufficiently large, this may causeunacceptable transient performance and e.g. result in a transientovervoltage until the power control loop can adapt the power level etc.In such a case, the operation of the power receiver 105 may be adaptedby the second configuration controller 609 in preparation for the powertransfer configuration change. For example, the input circuit may beisolated from sensitive circuitry which may be susceptible to theover-voltage condition. Specifically, in many embodiments, the may load603 may be disconnected.

The first receiver 305 may receive the power transfer configurationchange request message from the power receiver 105 and in response toreceiving this, the first configuration controller 309 may proceed toswitch the power transmitter 101 to the new candidate power transferconfiguration. In some embodiments, the power transfer configurationchange request message may indicate the power transfer configuration,such as e.g. indicate whether the power transmitter 101 is requested toswitch to a higher or lower maximum power limit. In other embodiments,this may be implicit, e.g. by there being only one candidate powertransfer configuration.

In the system, the change of the power transfer configuration is thusnot exclusively performed by the power transmitter 101 but is performedin collaboration between the power transmitter and the power receiver.The power receiver is not only informed of the possible impact of achange in the power transfer configuration but is also in control ofwhether there is a change in the power transfer configuration. Thus, thechange in power transfer configuration may in principle be initiated bythe power transmitter or the power receiver but the approach allows forthe power receiver to control whether the change in power transferconfiguration proceeds or not.

The approach may accordingly allow a flexible approach that effectivelycan support a large range of power levels by employing a range ofdifferent power transfer configurations with different voltages andmaximum power limits. The approach allows for this approach to be usedwith a large range of power transmitters and power receivers withoutrisking e.g. unacceptable overvoltage or undervoltage conditions.Rather, it can be ensured that a given change in power transferconfiguration only occurs in a way and if the change is acceptable tothe specific power receiver. The approach may thus allow the operationto be adapted to the specific power transmitter and power receiverinvolved.

The approach may also provide improved backwards compatibility and e.g.allow introduction to systems where some power receivers do not supportdifferent power transfer configurations. Such a power receiver will notcomprise functionality for generating and transmitting a power transferconfiguration change request message and accordingly the powertransmitter will not switch the power transfer configuration even if itwould consider it expedient to do so.

In some embodiments, the power configuration message may also provide anindication of the maximum power level of the power transferconfiguration(s) for which the voltage indication(s) is(are) provided.For example, the power configuration message may explicitly indicate themaximum power level by dedicated data, e.g. giving a value in Watts orproviding a reference to one out of a predetermined set of levels.

However, in many embodiments, the power configuration message may notcomprise any data defining a maximum power limit for the power transferconfiguration(s). In some such embodiments, the power configurationmessage may in itself be (implicitly) indicative of some informationabout the maximum power levels. For example, as indicated above, thepower configuration message may itself indicate whether there is indeeda higher and/or lower maximum power limit. In some embodiments, themaximum power limits for the set of power transfer configurations arepredetermined and known by the power receiver (or e.g. communicated tothe power receiver during power transfer initialization). In this case,the power receiver will know the maximum power limit for the next higherand the next lower power transfer configurations and thus the powerconfiguration message implicitly by providing a voltage indication alsoprovides an indication of the maximum power limits.

In many embodiments, the power configuration message may as mentionedspecifically provide a voltage amplitude for the power transferconfiguration which has maximum power limit being at least one of thenext higher maximum power limit or the next lower maximum power limitwith respect to the maximum power limit of the current power transferconfiguration, or in many embodiments advantageously the power transferconfiguration which has maximum power limit being at least one of thenext higher maximum power limit and the next lower maximum power limitwith respect to the maximum power limit of the current power transferconfiguration (thus the voltage amplitude may be provided for both thenext higher and the next lower power transfer configurations).

Thus, in many embodiments, the power configuration message may compriseinformation of the two power transfer configurations that correspond tothe next lower and higher power limit available. This may provide anefficient system in which power levels can be flexibly changed whilemaintaining a low complexity and communication bandwidth. For example,new data need only be communicated once a change in power transferconfiguration occurs and data is only required for one or two powertransfer configurations. In particular, the communication is limited tovery few parameters and there is no need to communicate data for allpower transfer configurations that are supported by the powertransmitter. This is a substantial advantage in practice ascommunication from the power transmitter to the power receiver is veryslow in wireless power transfer systems such as Qi.

The approach may also provide that step changes in voltage tend to berestricted to smaller steps. For example, a large change in power levelwill tend to be broken up into a plurality of smaller steps resulting insmaller transients.

In the example, the power transmitter accordingly informs the powerreceiver of the next higher or next lower voltage configuration beingavailable from the set of power transfer configurations supported by thepower transmitter. The power receiver can then request a switch to theavailable lower or higher configuration. As the power receiver requireshigher or lower power, it can step through the configurations. Thisavoids the power transmitter changing configuration unannounced, whichcould cause difficulties, or potentially even damage the power receiver.

In many embodiments, the indication of a voltage amplitude mayadvantageously be provided as a relative difference between the voltageamplitude for the candidate power transfer configuration and the voltageamplitude for the current power transfer configuration, and specificallyas the ratio between them. This may be particularly advantageous inembodiments where only the adjacent power transfer configurations areindicated as it may allow a normalization for the value that needs to becommunicated thereby allowing a more accurate representation for a givennumber of bits. For example, if the maximum step in voltage amplitudebetween adjacent power transfer configurations is a factor of, say, 2,the indication of the ratio needs to cover only a range from e.g. 1 to 2despite e.g. the set of power transfer configurations covering a voltageamplitude range of, say, a factor of 10.

An example of a possible power configuration message is illustrated inFIG. 7 . In the example, the power configuration message is named aPower Supply Configuration (PSC) data packet which is transmitted fromthe power transmitter to the power receiver. In the example, the PSCdata packet comprises two fields each being 8 bits. The first fieldincludes a Voltage Step Down data value and the second field includes aVoltage Step Up data value, where the first field indicates the relativechange in the voltage amplitude of the drive signal if the powertransmitter switches to the next lower power transfer configuration andthe second field indicates the relative change in the voltage amplitudeof the drive signal if the power transmitter switches to the next higherpower transfer configuration. As a specific example, the values may beprovided in accordance with the following protocol:

Voltage Step Down: The load voltage will decrease by 1/64 of this thisfactor on activating the next lower power transfer configuration (valuein the range of 64 . . . 255).

Voltage Step Up: The load voltage will increase by 1/64 of this factoron activating the next higher power transfer configuration (value in therange of 64 . . . 255).

In some embodiments, a predetermined value of the data field comprisingthe data indicating the voltage amplitude for a candidate power transferconfiguration may be used to indicate that the current power transferconfiguration is an extreme power transfer configuration in the sensethat it is the highest or lowest power level power transferconfiguration.

Thus, a predetermined value for the voltage amplitude data field of thepower configuration message may be used to indicate to the powerreceiver that the set of power transfer configurations supported by thepower transmitter does not include any power transfer configurationhaving a higher maximum power limit. Similarly, a (nother) predeterminedvalue for the voltage amplitude data field of the power configurationmessage may be used to indicate to the power receiver that the set ofpower transfer configurations supported by the power transmitter doesnot include any power transfer configuration having a higher maximumpower limit.

For example, for the PSC of FIG. 7 , a value of 0 in the fields mayindicate that there is no next higher or lower configuration available(i.e. a 0 in the Voltage Step Down field indicates that there is nolower power transfer configuration and a 0 in the Voltage Step Up fieldindicates that there is no higher power transfer configuration).

In some embodiments, a predetermined value of the data indicative of thevoltage amplitude is indicative of there being no change in the voltageamplitude for the candidate power transfer configuration relative to avoltage amplitude for a current power transfer configuration. Forexample, for the PSC message of FIG. 7 , a value of 64 can indicate thatthe voltage amplitude will not change (but the maximum power limit maychange).

It will also be appreciated that the power transfer configuration changerequest message may be in any suitable format or using any suitableprotocol. An example is provided in FIG. 8 . In this example, the powertransfer configuration change request message is named a SpecificReQuest/next configuration, SRQ/nc data packet which is transmitted fromthe power receiver to the power transmitter. In the example, the SRQ/ncmessage comprises an eight bit data field but only one data bit bo ofthis data field is used. This data bit indicates the direction of therequest, i.e. whether the request is for a power transfer configurationwith an increased or decreased maximum power limit.

In many embodiments, the power transmitter may further respond to thepower transfer configuration change request message and may specificallyin the response acknowledge the request. The response message mayspecifically indicate a timing of the change of the power transferconfiguration. The response message may specifically indicate a time forthe change or the timing of the response message may itself be anindication of the timing of the change of the power transferconfiguration. For example, the power transmitter may proceed to changethe power transfer configuration a predetermined time after thetransmission of the response message.

As a specific example, the response message may be one of the followingexamples:

ACK: The requested new power transfer configuration becomes activewithin TBD ms after acknowledging the SRQ/en data packet

NAK: The power transmitter has denied the request and continues to usethe current power transfer configuration (e.g. because the switch wouldresult in exceeding the power supply's capability at the currentoperating point).

In some embodiments, the power transmitter may initiate the potentialchange of the power transfer configuration.

For example, the first configuration controller 309 may be arranged totransmit the power configuration message in response to a detection thatan operating characteristic of the power transfer meets a criterion, andespecially in response to a detection that a current power level of thepower transmitter exceeds a threshold where the threshold is dependenton a maximum power limit of the current power transfer configuration.

For example, the first configuration controller 309 may continuouslymonitor the power level of the drive signal and compare it to themaximum power limit for the current power transfer configuration. If the(e.g. low pass filtered) power level of the drive signal exceeds, say,90% of the maximum power limit, the first configuration controller 309may consider that it is likely that it will be appropriate to switch toa power transfer configuration having a higher maximum power limit andit may accordingly proceed to transmit the power configuration message.

As another example, the first configuration controller 309 may monitorthe frequency of the drive signal and if this deviates too much from agiven resonance frequency of the resonance circuit comprising thetransmitter coil 103 (indicating that the drive signal is detunedsubstantially from the nominal operating point in order to reduce thepower of the power transfer signal for the current voltage amplitude)the power transmitter may proceed to transmit the power configurationmessage.

In this case, the transmission of the power configuration message isaccordingly not only providing information on the voltage amplitudes forcandidate power transfer configurations but also provides an indicationthat a change in power transfer configuration is desired/requested bythe power transmitter. E.g. in the above two examples, the powerconfiguration message may indicate a desire to switch to a highermaximum power limit power transfer configuration and a desire to switchto a lower maximum power limit power transfer configurationrespectively. In some such embodiments, the power configuration messagemay further include an indication whether a switch to a higher or lowermaximum power limit is desired.

In some embodiments, the power receiver may initiate the change in thepower transfer configuration. For example, similarly to the approachdescribed for the power transmitter, the second configuration controller609 may determine the currently extracted power level and compare it toa threshold reflecting the maximum power limit for the current powertransfer configuration. Alternatively or additionally, it may measurethe frequency of the power transfer signal and detect if this deviatestoo far from a nominal value.

The detection of such operating characteristics may be a detection of apower transfer configuration change preference and in response the powerreceiver may transmit a power configuration information request messageto the power transmitter. This message may in some embodiments be arequest for the power transmitter to transmit a power configurationmessage and accordingly the power transmitter may transmit the powerconfiguration message thereby providing the power receiver withinformation of the possibility for changing the power transferconfiguration as well as the associated consequence for the voltageamplitude.

A particular example of a possible message exchange of a power receiverinitiated change in power transfer configuration is shown in FIG. 9 anda possible message exchange of a power receiver initiated change inpower transfer configuration is shown in FIG. 10 . The examples includethe following messages:

CE (Power) Control Error, used by the power receiver to control itspower and voltage levels to appropriate target points.

RP/0 Received Power Packet, used by the power receiver to inform thepower transmitter about the amount of power it receives.

ACK Acknowledgement; used by the power transmitter to indicate that itaccepts a request.

NEGO Negotiation request; used by the power receiver to initiate anegotiation sequence.

GRQ/psc General ReQuest/power supply configuration; used by the powerreceiver to request the power transmitter to send a PSC message.

PSC Power Supply Configuration; used by the power transmitter tocommunicate parameters of the next higher and next lower powerconfigurations.

SRQ/nc Specific ReQuest/next configuration; used by the power receiverto request a next higher or next lower configuration.

SRQ/en Specific ReQuest/end negotiation; used by the power receiver toterminate the negotiation sequence and indicate that the negotiatedconfiguration should become active within TBD milliseconds.

In some embodiments, the power receiver may as previously mentioneddetermine whether the change in voltage amplitude associated with aswitch of the power transfer configuration will cause an unacceptableover- or undervoltage condition and only proceed to transmit the powertransfer configuration change request message if this is not the case.

In some embodiments, the power receiver may be arranged to compensatethe operation of the power receiver in advance of a switch in the powertransfer configuration such that the resulting voltage change becomesacceptable even if it were not without any change in operation.

For example, in advance of the change of the power transferconfiguration, the second configuration controller 609 may be arrangedto modify the power transfer operation to change the induced voltage ina direction opposite to the change in voltage that will occur in thesubsequent change in power transfer configuration.

For example, for a change which increases the voltage amplitude of thedrive signal, and thus which will result in an increased transientvoltage being induced in the receiver coil 107 when the change in powertransfer configuration occurs, the second configuration controller 609may in advance of the change proceed to reduce the induced voltage overthe receiver coil 107. When the change then occurs, the voltage over thereceiver coil 107 may increase but due to the previous voltagereduction, this increase may be acceptable and not result in e.g. adamaging overvoltage condition.

In some embodiments, the second configuration controller 609 may bearranged to change the load impedance prior to the switch in the powertransfer configuration, and specifically this change in load impedancemay be done together with the change in induced voltage.

For example, power transfer may be ongoing with a load of the powertransfer signal which is close to the maximum power limit for thecurrent power transfer configuration. Accordingly, there may be apreference to switch to the next higher maximum power limit and this maybe detected by the second configuration controller 609 (e.g. based onreceiving a power configuration message or based on it itself evaluatingthe power transfer characteristics). It may accordingly transmit a powertransfer configuration change request message to the power transmitterand at the same time proceed to reduce the impedance/resistanceresulting in a lower voltage and higher current providing the same powerlevel but at a lower voltage. After the change in the power transferconfiguration, the impedance may again be changed to suit the newconditions.

As a specific example, the previously described situation may beconsidered where the power transmitter may be operating in a 10 W (5 V,2 A) configuration, with the power receiver controlling its operatingpoint to 8 V, 1 A. When the power transmitter switches to a next higherconfiguration, such as 12 W (12V, 1 A), the power receiver wouldinitially see a voltage of 12/5*8=19.5 V, 2.4 A, which his far beyondthe capability of the power transmitter in this configuration.Accordingly, the power transfer may collapse due to the over voltage orover-power condition being generated. In order to prevent this situationfrom occurring, the power receiver would have to control its power levelback to e.g. 4 V, 0.5 A before making the switch. In the latter case,after the switch, the power receiver operates at 12*/5*4=9.6 V, 1.2 A(i.e. 11.5 W, assuming no losses).

A similar example when switching to a lower-power configuration may bewhere the power transmitter operates in a 12V, 1 A configuration, andthe power receiver takes only 4 W (e.g. 5 V, 0.8 A). The system may thenswitch to a next-lower configuration on the power transmitter, e.g. 5 V,1.5 A. Were this switch to be made without the power receiver preparing,it would experience a voltage of 5/12*5=2.1 V after the switch, whichcould be too low to sustain its operations (i.e. under voltage).Accordingly, this would result in a collapse of the power transfer aswell. However, this can be addressed by increasing the induced voltagein preparation of the switch.

The previous examples have focused on embodiments in which the voltageamplitude of the drive signal fed to the output circuit from the driveris constant for any given power transfer configuration. However, theapproach may also be suitable for embodiments in which the voltageamplitude is not constant while the power transmitter is operating in agiven power transfer configuration.

For example, in some embodiments, the power transmitter may be arrangedto operate within a given voltage amplitude range for each powertransfer configuration. For example, for each power transferconfiguration there may be a given maximum voltage amplitude and thuseach power transfer configuration may be associated with a differentcombination of a maximum power limit and a maximum voltage amplitude(limit) for the drive signal.

In such a case, the voltage amplitude indication being communicated bythe power configuration message may indicate the maximum voltageamplitude (limit) for the corresponding candidate power transferconfiguration. Accordingly, the power receiver may be arranged todetermine a maximum voltage transient or step that may occur whenswitching from the current power transfer configuration to the candidatepower transfer configuration. For example, when switching to a new powertransfer configuration, the power transmitter may always start at themaximum voltage amplitude and a power receiver keeping track of thecurrent voltage amplitude (e.g. by comparing the currently inducedvoltage to the voltage just after the power transmitter switched intothe current power transfer configuration) can determine the inducedvoltage amplitude immediately after the switch to the new power transferconfiguration.

Similarly, the voltage amplitude for a given power transferconfiguration may have a minimum limit, and the power configurationmessage may additionally or alternatively indicate the minimum voltageamplitude limit for a candidate power transfer configuration. This mayaccordingly allow the power receiver to determine the lowest inducedvoltage that will be experienced immediately after changing of the powertransfer configuration.

In some embodiments, the voltage amplitude indicated in powerconfiguration message may not be a maximum and/or minimum voltageamplitude limit but may e.g. be a nominal or initial voltage amplitude.For example, when switching power transfer configuration, the powertransmitter may be arranged to initiate the new power transferconfiguration with a given voltage amplitude for the drive signal, andthis initial voltage amplitude may be transmitted to the power receiverin the power configuration message. The power receiver can accordinglydetermine the induced voltage immediately after the switch of the powertransfer configuration, e.g. by considering the initial voltageamplitude for the candidate power transfer configuration in relation toa current voltage amplitude or in relation to the initial voltageamplitude for the current power transfer configuration. After theswitch, the voltage amplitude may subsequently be modified by the powertransmitter, but this will typically be so slow that no transients orsteps will be experienced by the power receiver.

The voltage amplitude may for example be indicated in the powerconfiguration message as a relative value with respect to e.g. theinitial voltage amplitude for the current power transfer configuration.In some embodiments, the voltage amplitude for the candidate powertransfer configuration may be provided as a relative indication withrespect to a current voltage amplitude. For example, the ratio betweenthe initial voltage amplitude for the candidate power transferconfiguration and the current voltage amplitude may be included in thepower configuration message. This may facilitate the power receiverdetermining the voltage step when switching power transfer configuration(e.g. it does not need to keep track of the variations in the voltageamplitude) and is typically feasible due to a very slow variation of thevoltage amplitude.

The approach of having a variable voltage amplitude may in particularallow or support implementations where the power level of the powertransfer signal is (at least partially) controlled by changing the drivesignal voltage amplitude. For example, it may allow an approach wherethe voltage amplitude of the drive signal is adapted based on powercontrol error messages from the power receiver.

It will be appreciated that the above description for clarity hasdescribed embodiments of the invention with reference to differentfunctional circuits, units and processors. However, it will be apparentthat any suitable distribution of functionality between differentfunctional circuits, units or processors may be used without detractingfrom the invention. For example, functionality illustrated to beperformed by separate processors or controllers may be performed by thesame processor or controllers. Hence, references to specific functionalunits or circuits are only to be seen as references to suitable meansfor providing the described functionality rather than indicative of astrict logical or physical structure or organization.

The invention can be implemented in any suitable form includinghardware, software, firmware or any combination of these. The inventionmay optionally be implemented at least partly as computer softwarerunning on one or more data processors and/or digital signal processors.The elements and components of an embodiment of the invention may bephysically, functionally and logically implemented in any suitable way.Indeed the functionality may be implemented in a single unit, in aplurality of units or as part of other functional units. As such, theinvention may be implemented in a single unit or may be physically andfunctionally distributed between different units, circuits andprocessors.

Although the present invention has been described in connection withsome embodiments, it is not intended to be limited to the specific formset forth herein. Rather, the scope of the present invention is limitedonly by the accompanying claims. Additionally, although a feature mayappear to be described in connection with particular embodiments, oneskilled in the art would recognize that various features of thedescribed embodiments may be combined in accordance with the invention.In the claims, the term comprising does not exclude the presence ofother elements or steps.

It will be appreciated that the reference to a preferred value does notimply any limitation beyond it being the value determined in the foreignobject detection initialization configuration, i.e. it is preferred byvirtue of it being determined in the adaptation process. The referencesto a preferred value could be substituted for references to e.g. a firstvalue.

Furthermore, although individually listed, a plurality of means,elements, circuits or method steps may be implemented by e.g. a singlecircuit, unit or processor. Additionally, although individual featuresmay be included in different claims, these may possibly beadvantageously combined, and the inclusion in different claims does notimply that a combination of features is not feasible and/oradvantageous. Also the inclusion of a feature in one category of claimsdoes not imply a limitation to this category but rather indicates thatthe feature is equally applicable to other claim categories asappropriate. Furthermore, the order of features in the claims do notimply any specific order in which the features must be worked and inparticular the order of individual steps in a method claim does notimply that the steps must be performed in this order. Rather, the stepsmay be performed in any suitable order. In addition, singular referencesdo not exclude a plurality. Thus, references to “a”, “an”, “first”,“second” etc. do not preclude a plurality. Reference signs in the claimsare provided merely as a clarifying example shall not be construed aslimiting the scope of the claims in any way.

The invention claimed is:
 1. A power transmitter comprising: an outputcircuit comprising a transmitter coil, wherein the output circuit isarranged to generate a power transfer signal in response to a drivesignal; a driver circuit, wherein the driver circuit is arranged togenerate the drive signal, wherein the drive signal is applied to theoutput circuit; a configuration controller circuit, wherein theconfiguration controller circuit is arranged to switch between at leasttwo of a set of power transfer configurations, wherein at least aportion of power transfer configurations from the set of power transferconfigurations have different combinations of a maximum power limit anda voltage amplitude of the drive signal; a transmitter circuit, whereinthe transmitter circuit is arranged to transmit a power configurationmessage to a power receiver, wherein the power configuration messagecomprises a first data, wherein the first data is indicative of avoltage amplitude for a first power transfer configuration, wherein thefirst power transfer configuration is one of the set of power transferconfigurations; and a receiver circuit, wherein the receiver circuit isarranged to receive a power transfer configuration change requestmessage from the power receiver, wherein the power transferconfiguration change request message comprises a request to change apower transfer configuration of the power transmitter, and wherein theconfiguration controller circuit is arranged to switch the powertransmitter circuit to the first power transfer configuration inresponse to the power transfer configuration change request message. 2.The power transmitter of claim 1, wherein the first data is indicativeof a relative difference between the voltage amplitude for the firstpower transfer configuration and a voltage amplitude for a current powertransfer configuration.
 3. The power transmitter of claim 2, wherein thefirst data is indicative of a ratio between the voltage amplitude forthe first power transfer configuration and the voltage amplitude for thecurrent power transfer configuration.
 4. The power transmitter of aclaim 1, wherein the first power transfer configuration has a maximumpower limit, wherein the maximum power limit is at least one of the nexthigher maximum power limit and the next lower maximum power limit inrelation to a maximum power limit of a current power transferconfiguration.
 5. The power transmitter of claim 1, wherein the powerconfiguration message comprises a second data, wherein the second datais indicative of a voltage amplitude for a second power transferconfiguration, wherein the second power transfer configuration is one ofthe set of power transfer configurations, wherein the first powertransfer configuration has a first maximum power limit, wherein thefirst maximum power limit is a next higher maximum power limit inrelation to a maximum power limit of a current power transferconfiguration, wherein the second power transfer configuration having asecond maximum power limit, wherein the second maximum power limit isthe next lower maximum power limit in relation to the maximum powerlimit of the current power transfer configuration.
 6. The powertransmitter of claim 1, wherein a predetermined value of the first dataindicates that the set of power transfer configurations does notcomprise a power transfer configuration that has a higher maximum powerlimit than a maximum power limit of a current power transferconfiguration.
 7. The power transmitter of claim 1, wherein theconfiguration controller circuit is arranged to transmit the powerconfiguration message in response to a detection that an operatingcharacteristic of the power transfer meets a criterion.
 8. The powertransmitter of claim 1, wherein the configuration controller circuit isarranged to transmit the power configuration message in response to adetection that a current power level of the power transmitter exceeds athreshold, wherein the threshold is dependent on a maximum power limitof a current power transfer configuration.
 9. The power transmitter ofclaim 1, wherein the configuration controller circuit is arranged totransmit the power configuration message in response to receiving apower configuration information request message from the power receiver.10. The power transmitter of claim 1, wherein configuration controllercircuit is arranged to switch the power transmitter to the first powertransfer configuration after having transmitted an acknowledgementmessage to the power receiver, wherein the acknowledgement messageacknowledges a request message received from the power receiver.
 11. Apower receiver comprising: an input circuit, wherein the input circuitcomprises a power receiver coil, wherein the power receiver coil isarranged to extract power from a power transfer signal; a receivercircuit, wherein the receiver circuit is arranged to receive a powerconfiguration message from a power transmitter, wherein the powerconfiguration message comprises data indicative of a voltage amplitudeof a drive signal for at least a first power transfer configuration,wherein the first power transfer configuration is one of a set of powertransfer configurations, wherein each of the set of power transferconfigurations have different combinations of a maximum power limit anda voltage amplitude, wherein the drive signal is applied to an outputcircuit of the power transmitter, wherein the output circuit comprises atransmitter coil, wherein the transmitter coil is arranged to generatethe power transfer signal in response to the drive signal; aconfiguration controller circuit, wherein the configuration controllercircuit is arranged to detect a power transfer configuration changepreference, wherein the power transfer configuration change preferenceindicates that the power transmitter is to switch to the first powertransfer configuration; and a transmitter circuit, wherein thetransmitter circuit is arranged to transmit a power transferconfiguration change request message to the power transmitter inresponse to the detection of the power transfer configuration changepreference, wherein the power transfer configuration change requestmessage comprises a request to change a power transfer configuration ofthe power transmitter, and wherein the power transfer configurationchange request message comprises a request for the power transmitter toswitch to the first power transfer configuration.
 12. The power receiverof claim 11, wherein the configuration controller circuit is arranged tocontrol the power transfer to change a voltage induced over the powerreceiver coil in advance of a change in power transfer configuration tothe first power transfer configuration.
 13. The power receiver of claim11 wherein the configuration controller circuit is arranged to change aload impedance of the power receiver coil in advance of a change inpower transfer configuration to the first power transfer configuration.14. A method of operating a power transmitter comprising: applying adrive signal to an output circuit; generating a power transfer signal inresponse to the drive signal; switching between at least two of a set ofpower transfer configurations, wherein each the set of power transferconfigurations have different combinations of a maximum power limit anda voltage amplitude of the drive signal; transmitting a powerconfiguration message to a power receiver, wherein the powerconfiguration message comprises a first data, wherein the first data isindicative of a voltage amplitude for a first power transferconfiguration, wherein the first power transfer configuration is one ofthe set of power transfer configurations; receiving a power transferconfiguration change request message from the power receiver, whereinthe power transfer configuration change request message comprises arequest to change a power transfer configuration of the powertransmitter; and switching the power transmitter to the first powertransfer configuration in response to the power transfer configurationchange request message.
 15. A method of operating a power receivercomprising: extracting power from a power transfer signal; receiving apower configuration message from a power transmitter, wherein the powerconfiguration message comprises a first data, wherein the first data isindicative of a voltage amplitude of a drive signal for at least a firstpower transfer configuration, wherein the first power transferconfiguration is one of a set of power transfer configurations, whereinthe power transfer configurations of the set of power transferconfigurations have different combinations of a maximum power limit anda voltage amplitude, wherein the drive signal is applied to an outputcircuit of the power transmitter, wherein the power transmitter isarranged to generate the power transfer signal in response to the drivesignal is applied to the output circuit; detecting a power transferconfiguration change preference, wherein the power transferconfiguration change preference indicates that for the power transmitteris to switch to the first power transfer configuration; and transmittinga power transfer configuration change request message to the powertransmitter in response to the detection of the power transferconfiguration change preference, wherein the power transferconfiguration change request message comprises a request to change apower transfer configuration of the power.
 16. A wireless power transfersystem comprising a power transmitter and a power receiver, the powertransmitter comprising: an output circuit comprising a transmitter coil,wherein the output circuit is arranged to generate the power transfersignal in response to a drive signal; a driver circuit, wherein thedriver circuit is arranged to generate the drive signal; a transmitterconfiguration controller circuit, wherein the transmitter configurationcontroller circuit is arranged to switch between at least two of a setof power transfer configurations, wherein at least a portion of thepower transfer configurations wherein from the set of power transferconfigurations have different combinations of a maximum power limit anda voltage amplitude of the drive signal; a first transmitter circuit,wherein the first transmitter circuit is arranged to transmit a powerconfiguration message to the power receiver, wherein the powerconfiguration message comprises a first data, wherein the first data isindicative of a voltage amplitude for a first power transferconfiguration, wherein the first power transfer configuration is one ofthe set of power transfer configurations; and a first receiver circuit,wherein the first receiver circuit is arranged to receive a powertransfer configuration change request message from the power receiver,wherein the configuration controller circuit is arranged to switch thepower transmitter circuit to the first power transfer configuration inresponse to the power transfer configuration change request message; thepower receiver comprising: an input circuit, wherein the input circuitcomprises a power receiver coil, wherein the power receiver coil isarranged to extract power from the power transfer signal; a secondreceiver circuit, wherein the second receiver circuit is arranged toreceive the power configuration message from the power transmitter, areceiver configuration controller circuit, wherein the receiverconfiguration controller circuit is arranged to detect a power transferconfiguration change preference for the power transmitter to switch tothe first power transfer configuration; and a second transmittercircuit, wherein the second transmitter circuit is arranged to transmitthe power transfer configuration change request message to the powertransmitter in response to the detection of the power transferconfiguration change preference, and wherein the power transferconfiguration change request message comprises a request to change apower transfer configuration of the power transmitter.
 17. Anon-transitory computer readable medium having stored thereoninstructions that when executed by processing circuitry of a powertransmitter causes the power transmitter to perform the method asclaimed in claim
 14. 18. A non-transitory computer readable mediumhaving stored thereon instructions that when executed by processingcircuitry of a power receiver causes the power receiver to perform themethod as claimed in claim
 15. 19. The method of operating a powertransmitter of claim 14, wherein the power configuration messagecomprises a second data, wherein the second data is indicative of avoltage amplitude for a second power transfer configuration, wherein thesecond power transfer configuration is one of the set of power transferconfigurations, wherein the first power transfer configuration has afirst maximum power limit, wherein the first maximum power limit is anext higher maximum power limit in relation to a maximum power limit ofa current power transfer configuration, wherein the second powertransfer configuration having a second maximum power limit, wherein thesecond maximum power limit is the next lower maximum power limit inrelation to the maximum power limit of the current power transferconfiguration.
 20. The method of operating a power receiver of claim 15,wherein the power configuration message comprises a second data, whereinthe second data is indicative of a voltage amplitude for a second powertransfer configuration, wherein the second power transfer configurationis one of the set of power transfer configurations, wherein the firstpower transfer configuration has a first maximum power limit, whereinthe first maximum power limit is a next higher maximum power limit inrelation to a maximum power limit of a current power transferconfiguration, wherein the second power transfer configuration having asecond maximum power limit, wherein the second maximum power limit isthe next lower maximum power limit in relation to the maximum powerlimit of the current power transfer configuration.